Method for Treating Inkjet Liquid, Recording Apparatus Using the Same, Liquid Storage Tank, Liquid Absorber for Liquid Storage and Liquid Treatment Apparatus

ABSTRACT

The present invention relates to a method for treating liquids used in inkjet recording comprising, providing a first printing liquid and a second printing liquid that is capable of reacting with the first printing liquid to cause coagulation and thickening if mixed with the first printing liquid, and exposing the first and second printing liquids to each other to form a mixture, wherein when the mixture includes a coagulation-thickening preventing agent which prevents the reaction of the printing liquids.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 USC 119 from Japanese patentApplication No. 2003-295926, the disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to a method oftreating an inkjet liquid (printing liquid) such as an ink or aprocessing liquid used in printing with an inkjet recording apparatus.Further, the invention relates to an inkjet recording apparatus, aninkjet liquid storage tank, and liquid absorber for inkjet liquidstorage and an inkjet liquid treatment apparatus using the method.

2. Description of the Related Art

In inkjet recording methods, a liquid or melt solid ink is fired fromnozzles, slits, porous films and the like, to perform recording onpaper, cloth, film and the like. These methods have features of smallsize, low cost and silence and are used in a lot of printers. Amongthem, a piezo inkjet method of firing a liquid ink from a nozzleutilizing deformation of a piezoelectric element and a heat inkjetmethod which utilizes a heat boiling phenomenon are excellent inresolution and printing speed. Therefore, these methods are frequentlyutilized.

Inkjet recording is a promising recording technology as described above,however, it has a problem of poor discharge of ink. There are variouscauses for poor discharge, and drying and thickening of an ink in anozzle, and clogging of a nozzle with bubble, refuse and the like can beexemplified. As technologies developed for solving such problems, atechnology of covering a nozzle with a cap during non-printing period, atechnology of providing a suction apparatus for discharging thickenedinks, bubbles and refuses, a technology of empty firing, so-called dummyjet, and the like, can be exemplified. Among suggested technologies aretechnologies of providing an ink suction mechanism (see, Japanese PatentApplication Laid-Open (JP-A) Nos. 56-60256, 57-12655, 62-113556 and63-295265) and a technology of wiping off an ink adhered on the endsurface of a head body by a wiper member (JP-A No. 62-251146). Owing todevelopment of such technologies, improvement in poor discharge has beentried.

On the other hand, it has been recently desired to print at high speedand with high image quality particularly on regular paper. Therefore,various methods have been suggested to improve image density and toimprove bleed of a single color and inter-color bleed. In a methodsuggested in JP-A No. 6-106735, in an ink set, color inks contains asurfactant that promotes permeation, and a solvent and salt, and theblack ink contains a component causing thickening or coagulation underan influence of a salt. In a method suggested in JP-A No. 10-272768, pHof a color ink is 5 or lower, coagulation of a black ink is caused bycontact of a black ink having weak ion strength with a color ink havingstrong ion strength, to improve water resistance and inter-color bleed.Examples of the compound enhancing the ion strength of a color ink inthis method include monovalent and polyvalent chlorides, fluorides,bromides, nitrates and tosylates of alkali metals and alkaline earthmetals.

However, when components thus causing coagulation are used in inks andprocessing liquids, in the maintenance part including a disposalapparatus that disposes of an ink and processing liquid, it is necessaryto dispose of inks and processing liquids separately if the inks and theprocessing liquids cause coagulation and thickening when mixed.Consequently, an inkjet recording apparatus becomes larger and the costincreases.

There is a maintenance part that fires inks and processing liquids fromeach nozzle immediately before formation of an image (dummy jet) andprevent the discharge at the formation of an image from becoming faulty.There is also a method in which a cap is provided on each head toprevent drying of inks and processing liquids in a nozzle part, and theinks and the processing liquids are sucked by a pump while the nozzlesare capped, to remove from a nozzle inks and processing liquids thatwere thickened when they dried. In these example, usually, a wasteliquid composed of inks and processing liquids generated duringmaintenance is recovered through a tube to a waste ink tank that storesa waste liquid. In many cases, in the waste ink tank, a porous body suchas urethane foam or a fibrous material such as polyester felt is used asan absorber, and this absorber absorbs the waste liquid composed of inksand processing liquids.

If the inks and the processing liquid which coagulate or thicken whenmixed are mixed and disposed of in a part of disposal device in such amaintenance section, a problem occurs. For example, clogging with acoagulated substance occurs in a pump that sucks inks and processingliquids. Clogging with a coagulated substance occurs at the inlet orinside of a tube which is a route to a waste ink tank. Coagulationoccurs in the upper or other specific part of an absorber provided in awaste ink tank to disturb absorption of inks and processing liquids. Inthat case, the absorber and the waste ink tank can store less wasteliquid than expected. Because of these problem, the respective partscannot function well and the apparatus becomes faulty.

In order to avoid these problems, when there are two or morecombinations of printing liquids (ink-ink, ink-processing liquid) thatcan coagulate or cause coagulated substance when mixed, it is necessaryto provide waste liquid processing parts separately for each combinationof the printing liquids in a maintenance part. However, as a result, thenumber of parts of a waste liquid processing parts increases to elevatethe cost and the machine size also increases. There is therefore a needfor improved techniques for the treatment and disposal of liquids usedin inkjet recording.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentionedcircumstances. The invention relates to an inkjet liquid treatmentmethod and, an inkjet recording apparatus, inkjet liquid storing tank,liquid absorber for inkjet liquid storage and inkjet liquid treatmentapparatus using this method.

A first aspect of the invention is to provide a method for treatingliquids used in inkjet recording comprising:

providing a first printing liquid;

providing a second printing liquid that is capable of causingcoagulation if mixed with the first printing liquid; and

exposing the first and second printing liquids to each other to form amixture;

wherein the mixture includes a coagulation-thickening preventing agentwhich prevents the coagulation.

A second aspect of the invention is to provide a method for treatingliquids used in inkjet recording comprising:

providing a first printing liquid including a polyvalent metal ion and asecond printing liquid including an anionic compound that is capable ofreacting with the metal ion to cause coagulation and thickening if theanionic compound is mixed with the first printing liquid; and

exposing the first and second printing liquids to each other to form amixture,

wherein the mixture includes a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound.

A third aspect of the invention is to provide a method for treatingliquids used in inkjet recording comprising:

using an inkjet recording apparatus, wherein the apparatus uses at leastone first printing liquid including a polyvalent metal ion and at leastone second printing liquid including an anionic compound which iscapable of reacting with the metal ion to cause coagulation andthickening if mixed with the first printing liquid,

wherein the apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device having a liquid storage part that        recovers the printing liquids fired from the recording head        during a non-printing period and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the one second printing liquid(s) discharged fromthe recording head during the non-printing period is stored in theliquid storage part,

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

A fourth aspect of the invention is to provide an inkjet recordingapparatus which uses at least one first printing liquid including apolyvalent metal ion and at least one second printing liquid includingan anionic compound which is capable of reacting with the metal ion tocause coagulation and thickening if mixed with the first printingliquid, the apparatus comprising:

a recording head comprising a plurality of nozzles which fire at leastone liquid;

and a liquid treatment device having a liquid storage part that recoversthe printing liquids fired from the recording head during a non-printingperiod and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part, and

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

A fifth aspect of the invention is to provide an inkjet liquid storagetank used in an inkjet recording apparatus,

wherein the apparatus uses at least one first printing liquid includinga polyvalent metal ion and at least one second printing liquid includingan anionic compound which is capable of reacting with the metal ion tocause coagulation and thickening if mixed with the first printingliquid,

wherein the apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device comprising at least a liquid        storage tank that recovers the printing liquids discharged from        the recording head during a non-printing period and stores the        printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) discharged from therecording head during the non-printing period is stored in the liquidstorage tank, and

wherein the tank contains a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound,the agent being contained in a state which allows the agent to mix withthe mixture.

A sixth aspect of the invention is to provide a liquid absorber for aninkjet liquid storage used in an inkjet recording apparatus,

wherein the apparatus uses at least one first printing liquid includinga polyvalent metal ion and at least one second printing liquid includingan anionic compound which is capable of reacting with the metal ion tocause coagulation and thickening if mixed with the first printingliquid,

wherein the apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device having a liquid storage part that        recovers the printing liquids discharged from the recording head        during a non-printing period in order to maintain the recording        head and stores the printing liquids,

wherein the liquid storage part includes at least a liquid absorber forinkjet liquid storage, the absorber being able to store the at least oneliquid fired from the nozzles,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part, and

wherein the tank contains a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound,the agent being contained in a state which allows the agent to mix withthe mixture.

A seventh aspect of the invention is to provide an inkjet liquidtreatment apparatus used in an inkjet recording apparatus which uses atleast one first printing liquid including a polyvalent metal ion and atleast one second printing liquid including an anionic compound which iscapable of reacting with the metal ion to cause coagulation andthickening if mixed with the first printing liquid,

wherein the inkjet recording apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device having a liquid storage part that        recovers the printing liquids fired from the recording head        during a non-printing period and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part,

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

DESCRIPTION OF THE INVENTION

One embodiment of the present invention is a method for treating liquidsused in inkjet recording comprising:

providing a first printing liquid;

providing a second printing liquid that is capable of causingcoagulation if mixed with the first printing liquid; and

exposing the first and second printing liquids to each other to form amixture;

wherein the mixture includes a coagulation-thickening preventing agentwhich prevents the coagulation.

Another embodiment of the present invention is a method for treatingliquids used in inkjet recording comprising:

providing a first printing liquid including a polyvalent metal ion and asecond printing liquid including an anionic compound that is capable ofreacting with the metal ion to cause coagulation and thickening if theanionic compound is mixed with the first printing liquid; and

exposing the first and second printing liquids to each other to form amixture,

wherein the mixture includes a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound.

In this embodiment, the coagulation-thickening preventing agent may be achelating agent that chelates the metal ion or a masking agent thatmasks the metal ion and protects it from the anionic compound.

When the coagulation-thickening preventing agent is a chelating agentthat chelates the metal ion or a masking agent that masks the metal ionand protects it from the anionic compound, the coagulation-thickeningpreventing agent may be used in a form of a solution in a liquidcontaining a non-volatile organic solvent and water.

When the coagulation-thickening preventing agent is a chelating agentthat chelates the metal ion or a masking agent that masks the metal ionand protects it from the anionic compound and the coagulation-thickeningpreventing agent is used in a form of a solution in a liquid containinga non-volatile organic solvent and water, the coagulation-thickeningpreventing agent may contain a surfactant.

When the coagulation-thickening preventing agent is a chelating agentthat chelates the metal ion or a masking agent that masks the metal ionand protects it from the anionic compound and the coagulation-thickeningpreventing agent is used in a form of a solution in a liquid containinga non-volatile organic solvent and water and the coagulation-thickeningpreventing agent contains a surfactant, the non-volatile organic solventmay be at least one selected from poly-hydric alcohols and glycolethers.

The coagulation-thickening preventing agent may be at least one selectedfrom the group consisting of nitrilotriacetic acid,N,N-(2-hydroxyethyl)-glycine, ethylenediamine-N,N,N′,N′-tetraaceticacid, dicarboxylic acid, tricarboxylic acid, phosphoric acid and saltsthereof.

When the coagulation-thickening preventing agent is at least oneselected from the group consisting of nitrilotriacetic acid,N,N-(2-hydroxyethyl)-glycine, ethylenediamine-N,N,N′,N′-tetraaceticacid, dicarboxylic acid, tricarboxylic acid, phosphoric acid and saltsthereof, the dicarboxylic acid and salts thereof may be at least oneselected from tartaric acids consisting of tartaric acid, potassiumtartrate and sodium potassium tartrate, and the tricarboxylic acid andsalts thereof may be at least one selected from citric acids consistingof citric acid, lithium citrate, potassium citrate, potassium dihydrogencitrate, sodium citrate, disodium hydrogencitrate and triammoniumcitrate.

The content of the polyvalent metal ion contained in the first printingliquid may be 100 ppm or higher.

The content of the polyvalent metal ion contained in the first printingliquid may be 500 ppm or higher.

The polyvalent metal ion may be at least one selected from the groupconsisting of Mg, Ca, Ba, Cu, Co, Ni, Zn, Fe, Al, La, Nd, Y, Pr, Sm, Sband In ions.

The polyvalent metal ion may be a Mg ion.

The anionic compound may be an anionic colorant.

Two or more inks containing colorants may be used as the printingliquid.

At least one ink containing a colorant and at least one processingliquid may be used as the printing liquids.

Another embodiment of the invention is a method for treating liquidsused in inkjet recording comprising:

using an inkjet recording apparatus, wherein the apparatus uses at leastone first printing liquid including a polyvalent metal ion and at leastone second printing liquid including an anionic compound which iscapable of reacting with the metal ion to cause coagulation andthickening if mixed with the first printing liquid,

wherein the apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device having a liquid storage part that        recovers the printing liquids fired from the recording head        during a non-printing period and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the one second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part,

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

Another embodiment of the invention is an inkjet recording apparatuswhich uses at least one first printing liquid including a polyvalentmetal ion and at least one second printing liquid including an anioniccompound which is capable of reacting with the metal ion to causecoagulation and thickening if mixed with the first printing liquid, theapparatus comprising:

a recording head comprising a plurality of nozzles which fire at leastone liquid;

and a liquid treatment device having a liquid storage part that recoversthe printing liquids fired from the recording head during a non-printingperiod and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part, and

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

In this embodiment, the liquid storage part may contain a liquidabsorber.

The liquid storage part may contain a liquid storage tank.

The liquid treatment device may have only one one-chamber type liquidstorage part that stores all kinds of printing liquids fired from therecording head in a mixed state.

When the liquid treatment device has only one one-chamber type liquidstorage part that stores all kinds of printing liquids fired from therecording head in a mixed state, the liquid treatment device may haveonly one liquid recovering pipe that recovers all kinds of printingliquids fired from the recording head in a mixed and transfers themixture into the one-chamber type liquid storage part.

The coagulation-thickening preventing agent may be included in theliquid storage part in a state that enables the agent to mix with themixture including both the first and second printing liquids. The agentmay exist in the liquid storage part before the mixture enters the part.

The inkjet recording apparatus may include a device that adds acoagulation-thickening preventing agent to at least one liquid selectedfrom the mixture including both the first and second printing liquids,the first printing liquid before mixed with the second printing liquid,and the second printing liquid before mixed with the first printingliquid, at any time after firing of at least one of the first printingliquid and the second printing liquid from the recording head.

The inkjet recording apparatus may include a device that adds acoagulation-thickening preventing agent to the first printing liquidbefore mixed with the second printing liquid at any time after dischargeof the first printing liquid from the recording head.

When the inkjet recording apparatus comprises a device that adds acoagulation-thickening preventing agent to at least one liquid selectedfrom the mixture including both the first and second printing liquids,the first printing liquid before mixed with the second printing liquid,and the second printing liquid before mixed with the first printingliquid at any time after firing of at least one of the first printingliquid and the second printing liquid from the recording head, thedevice may be a liquid firing device having a nozzle that fires a liquidincluding the coagulation-thickening preventing agent dissolved therein.

The following constitution is possible: the recording head is providedwith a plurality of nozzles that fires at least two liquids separately,at least one of the liquids is the printing liquid, and at least one ofthe other liquids includes the coagulation-thickening preventing agentdissolved therein.

Another embodiment of the invention is an inkjet liquid storage tankused in an inkjet recording apparatus,

wherein the apparatus uses at least one first printing liquid includinga polyvalent metal ion and at least one second printing liquid includingan anionic compound which is capable of reacting with the metal ion tocause coagulation and thickening if mixed with the first printingliquid,

wherein the apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device comprising a liquid storage tank        that recovers the printing liquids fired from the recording head        during a non-printing period and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage tank, and

wherein the tank contains a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound,the agent being contained in a state which allows the agent to mix withthe mixture.

Another embodiment of the invention is a liquid absorber for an inkjetliquid storage used in an inkjet recording apparatus, wherein theapparatus uses at least one first printing liquid including a polyvalentmetal ion and at least one second printing liquid including an anioniccompound which is capable of reacting with the metal ion to causecoagulation and thickening if mixed with the first printing liquid,

wherein the apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device having a liquid storage part that        recovers the printing liquids fired from the recording head        during a non-printing period in order to maintain the recording        head and stores the printing liquids,

wherein the liquid storage part includes a liquid absorber for inkjetliquid storage, the absorber being able to store the at least one liquidfired from the nozzles,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part, and

wherein the tank contains a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound,the agent being contained in a state which allows the agent to mix withthe mixture.

Another embodiment of the invention is an inkjet liquid treatmentapparatus used in an inkjet recording apparatus which uses at least onefirst printing liquid including a polyvalent metal ion and at least onesecond printing liquid including an anionic compound which is capable ofreacting with the metal ion to cause coagulation and thickening if mixedwith the first printing liquid,

wherein the inkjet recording apparatus comprises:

-   -   a recording head comprising a plurality of nozzles which fire at        least one liquid;    -   and a liquid treatment device having a liquid storage part that        recovers the printing liquids fired from the recording head        during a non-printing period and stores the printing liquids,

wherein a mixture including at least one of the first printing liquid(s)and at least one of the second printing liquid(s) fired from therecording head during the non-printing period is stored in the liquidstorage part,

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

The liquid storage tank, the liquid absorber, or the liquid storage partmay include the coagulation-thickening preventing agent even before themixture including both the first and second printing liquids enter thetank or the storage part or contact the absorber, or even before themaintenance is conducted.

According to the invention, an inkjet liquid treatment method capable ofsuppressing coagulation and thickening even when two or more printingliquids which can coagulate and thicken when mixed are exposed to eachother and, an inkjet recording apparatus, an inkjet liquid storing tank,a liquid absorber for inkjet liquid storage, and an inkjet liquidtreatment apparatus using this method, can be provided. In thefollowing, the invention is described with reference to a specificcombination of compounds in the printing liquids which can causecoagulation or thickening when mixed. However, the invention is notlimited to the specific combination and other combinations can also beapplied.

(Inkjet Liquid Treatment Method)

The inkjet liquid treatment method of the invention is a methodcomprising providing a first printing liquid including a polyvalentmetal ion and a second printing liquid including an anionic compoundthat is capable of reacting with the metal ion to cause coagulation andthickening when mixed with the first printing liquid, exposing the firstand second printing liquids to each other to form a mixture,

wherein the mixture includes a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound.

Therefore, according to the inkjet liquid treatment method of theinvention, coagulation and thickening of the mixture can be suppressedeven when two or more printing liquids that can coagulate and thickenwhen mixed are treated in a mixed state.

Such an inkjet liquid treatment method of the invention may be usedparticularly preferably in an inkjet recording apparatus using the firstprinting liquid and the second printing liquid in combination as aprinting liquid.

When the inkjet liquid treatment method of the invention is used in aninkjet recording apparatus, it is preferable to utilize an inkjetapparatus having a constitution described below.

The inkjet recording apparatus may be preferably an inkjet recordingapparatus using at least one first printing liquid and at least onesecond printing liquid and comprising a recording head that comprises aplurality of nozzles firing at least one liquid and a liquid treatmentdevice that comprises a liquid storage part recovering the printingliquids fired from the recording head during a non-printing period andstoring the printing liquids,

wherein the liquid storage part can store a mixture which includes atleast one of the first printing liquid(s) and at least one of the secondprinting liquid(s) fired from the recording head during the non-printingperiod.

In this inkjet recording apparatus, the mixture stored in the liquidstorage part includes a coagulation-thickening preventing agent. Thecoagulation-thickening preventing agent included in the mixture storedin the liquid storage part can be added at any time after the firstprinting liquid and second printing liquid are fired from a recordinghead in a non-printing period such as maintenance but before bothliquids are mixed and finally stored in the liquid storage part.However, the agent may be added in periods other than the perioddescribed above.

Details of the method of adding a coagulation-thickening preventingagent are described below including also a specific constitution of aninkjet recording apparatus to which an inkjet liquid treatment method ofthe invention is applied.

In the inkjet recording apparatus, clogging in parts of the apparatusthat collects disposes of printing liquids can be prevented even when afirst printing liquid and second printing liquid fired from a recordinghead in a non-printing period are mixed. Further, it is not necessary toprovide separate members and apparatuses relating to treatment ofprinting liquids for every combination of printing liquids even if eachcombination can coagulate and thicken when mixed with any of the othercombinations. Therefore, the constitution of these members andapparatuses can be simplified and its size can be reduced. The cost canalso be reduced.

Although the inkjet liquid treatment method of the invention may be usedparticularly preferably in the inkjet recording apparatus as describedabove, the application of the invention is not limited to the apparatus.Of course, the method can be applied, if necessary, also when a printingliquid is treated outside the inkjet apparatus. The method can be used,for example when the following printing liquids are treated together:printing liquids in ink cartridges recovered from retail stores afterthe expiration of usable period; printing liquids in ink cartridgesdisposed of unused; printing liquids in ink cartridges which have beenleft in bad environments and has become unusable; printing liquids in areplenishing ink bottle; and the like. The method may be used fordisposal of waste liquids used in inkjet recording. Therefore, thecoagulation-thickening preventing agent may be included in the mixturewhen printing liquids are recovered and disposed of.

Next, the printing liquid and coagulation-thickening preventing agentused in the inkjet liquid treatment method of the invention aredescribed in more detail.

—Printing Liquid—

Regarding the printing liquid used in the inkjet liquid treatment methodof the invention, the two kinds of printing liquids (first printingliquid and second printing liquid) must be used in combination, whichwill be mixed, for example at the time of their disposal.

The first printing liquid includes a polyvalent metal ion and the secondprinting liquid includes an anionic compound that is capable of reactingwith the metal ion contained in the first printing liquid to causecoagulation or thickening or both when mixed with the first printingliquid.

These first and second printing liquids each are used as an inkincluding a colorant or a processing liquid which includes no colorantand which prevents inter-color bleed when the ink is provided onto thesurface of a recording medium. In this case, the first printing liquidmay be used as the ink or the processing liquid and the second printingliquid may be used as the ink or the processing liquid.

In the case of an inkjet recording apparatus, preferably, at least twoof the printing liquids used is used as inks, or at least one of them(but not all of them) is used as an ink and the other of them is used asa processing liquid.

Various components contained in a printing liquid, namely, thepolyvalent metal ion, the anionic compound, colorants, and othercomponents are described below.

—Polyvalent Metal Ion—

The polyvalent metal ion contained in a first printing liquid is notparticularly restricted providing it is a known polyvalent metal ion,and examples thereof include Mg, Ca, Ba, Cu, Co, Ni, Zn, Fe, Al, La, Nd,Y, Pr, Sm, Sb and In. These metal ions can be added to a first printingliquid in a form of a salt. Examples of the salt include phosphates,sulfates, nitrates, and acetates. The salt may have a solubility ofpreferably more than 10 in order to suppress deposition thereof in afirst printing liquid. When the solubility is 10 or less, clogging at anozzle part in a recording head occurs and the long-term stability ofthe ink deteriorates in some cases.

As the polyvalent metal ion, Mg is particularly preferable among theabove-mentioned metal ions. When Mg is used, secondary problems such asgeneration of clogging at a nozzle part of a recording head do not occureasily as compared with the other metal ions. Therefore, printingstability is improved.

The concentration of the polyvalent metal ion contained in a firstprinting liquid may be preferably 100 ppm or higher, more preferably 500ppm or higher. When the concentration of the polyvalent metal ioncontained in a first printing liquid is lower than 100 ppm, the effectsowing to metal ions described above such as improvement in waterresistance and suppression of inter-color bleed cannot be obtainedsufficiently and an image density lowers in some cases.

—Anionic Compound—

The anionic compound contained in a second printing liquid is notparticularly restricted providing it is capable of reacting with apolyvalent metal ion contained in the first printing liquid to causecoagulation or thickening or both. Specifically, anionic colorants andanionic polymer additives can be cited as examples. These specificexamples will be described below.

—Colorant—

When the printing liquid is used as an ink, known colorants (pigments,dyes) are added. As the colorant added to a first printing liquid,cationic colorants are used, and as the colorant added to a secondprinting liquid, anionic colorants are used.

The dyes may be water-soluble dyes or disperse dyes. Specific examplesof the water-soluble dyes include C. I. Direct Black-2, -4, -9, -11,-17, -19, -22, -32, -80, -151, -154, -168, -171, -194, -195, C. I.Direct Blue -1, -2, -6, -8, -22, -34, -70, -71, -76, -78, -86,-112,-142, -165, -199, -200, -201, -202, -203, -207, -218, -236, -287, -307-,C. I. Direct Red-1, -2, -4, -8, -9, -11, -13, -15, -20, -28, -31, -33,-37, -39, -51, -59, -62, -63, -73, -75, -80, -81, -83, -87, -90, -94,-95, -99, -101, -110, -189, -227, C. I. Direct Yellow-1, -2, -4, -8,-11, -12, -26, -27, -28, -33, -34, -41, -44, -48, -58, -86, -87, -88,-132, -135, -142, -144, -173, C. I. Food Black -1, -2, C. I. AcidBlack-1, -2, -7, -16, -24, -26, -28, -31, -48, -52, -63, -107, -112,-118, -119, -121, -156, -172, -194, -208, C. I. Acid Blue-1, -7, -9,-15, -22, -23, -27, -29, -40, -43, -55-, -59, -62, -78, -80, -81, -83,-90, -102, -104, -111, -185, -249, -254, C. I. Acid Red-1, -4, -8, -13,-14, -15, -18-, -21, -26, -35, -37, -52, -110, -144, -180, -249, -257,-289, C. I. Acid Yellow-1, -3, -4, -7, -11, -12, -13, -14, -18, -19,-23, -25, -34, -38, -41, -42, -44, -53, -55, -61, -71, -76, -78, -79,and C. I. Acid Yellow-122.

Specific examples of the disperse dyes include C. I. Disperse Yellow-3,-5, -7, -8, -42, -54, -64, -79, -82, -83, -93, -100, -119, -122, -126,-160, -184:1, -186, -198, -204, -224, C. I. Disperse Orange-13, -29,-31:1, -33, -49, -54, -66, -73, -119, -163, C. I. Disperse Red-1, -4,-11, -17, -19, -54, -60, -72, -73, -86, -92, -93, -126, -127, -135,-145, -154, -164, -167:1, -177, -181, -207, -239, -240, -258, -278,-283, -311, -343, -348, -356, -362, C. I. Disperse Violet-33, C. I.Disperse Blue -14, -26, -56, -60, -73, -87, -128, -143, -154, -165,-165:1, -176, -183, -185, -201, -214, -224, -257, -287, -354, -365,-368, C. I. Disperse Green-6:1 and -9.

Pigments can also be used. Specific examples of the black pigmentinclude, however not limited to, RAVEN 7000, RAVEN 5750, RAVEN 5250,RAVEN 5000 ULTRA II, RAVEN 3500, RAVEN 2000, RAVEN 1500, RAVEN 1250,RAVEN 1200, RAVEN 1190 ULTRA II, RAVEN 1170, RAVEN 1255, RAVEN 1080,RAVEN 1060 (these are manufactured by Columbian Carbon), REGAL 1400R,REGAL 1330R, REGAL 1660R, MOGUL L, BLACK PEARLS L, MONARCH 700, MONARCH800, MONARCH 880, MONARCH 900, MONARCH 1000, MONARCH 1100, MONARCH 1300,MONARCH 1400 (these are manufactured by Cabot Corporation), Color BlackFW1, Color Black FW2, Color Black FW2V, Color Black 18, Color BlackFW200, Color Black S150, Color Black S160, Color Black S170, PRINTEX 35,PRINTEX U, PRINTEX V, PRINTEX 140U, PRINTEX 140V, Special Black 6,Special Black 5, Special Black 4A, Special Black 4 (these aremanufactured by Degussa), No. 25, No. 33, No. 40, No. 47, No. 52, No.900, No. 2300, MCF-88, MA600, MA7, MA8, and MA100 (these aremanufactured by Mitsubishi Chemical Co., Ltd.).

Pigments obtained by conducting surface modification treatment on thepigments can be used as examples of the pigments which areself-dispersible in water. Other examples of usable pigment which isself-dispersible in water include CAB-O-JET-200, CAB-O-JET-300, IJX-253,IJX-266, IJX-444, IJX-273 and IJX-55 manufactured by Cabot Corporation,Microjet Black CW-1 and CW-2 manufactured by Orient Chemical Industries,Ltd., and commercially available self-disperse pigments such asself-disperse pigments marketed from Nippon Shokubai Co., Ltd.

Examples of the cyan ink pigment include, however not limited to, C. I.Pigment Blue-1, -2, -3, -15, -15:1, -15:2, -15:3, -15:4, -16, -22 and-60.

Examples of the magenta ink pigment include, however not limited to, C.I. Pigment Red-5, -7, -12, -48, -48:1, -57, -112, -122, -123, -146,-168, -184 and -202.

Examples of the yellow ink pigment include, however not limited to, C.I. Pigment Yellow -1, -2, -3, -12, -13, -14, -16, -17, -73, -74, -75,-83, -93, -95, -97, -98, -114, -128, -129, -138, -151- and -154.

As the colorants of respective colors, so-called capsule dyes andpigments obtained by capsulation of colorants with various resins may beused.

Particularly, from the viewpoint of obtaining an excellent image, it ispreferable to use, in combination, a black ink (second printing liquid)including as a colorant an anionic dye or carbon black having an anionicsurface group, and a color ink (first printing liquid) including thepolyvalent metal ion in a total amount of 500 ppm or more. In thiscombination, owing to the use of a black ink and a color ink together ina black ink image part, the image density increases, the inter-colorbleed at a part where a black image and a color image are adjacent issuppressed, and the image quality is improved.

—Other Additives—

The printing liquid contains water as a solvent in addition to theabove-mentioned components, and further, a water-soluble organic solventcan be added. When a water-soluble organic solvent is added to aprinting liquid, the moisture retaining property of an ink andprocessing liquid and the solubility of a colorant are further improved.As a result, clogging can be prevented, discharge stability at the timeof firing of a printing liquid from a recording head can be maintained.Further, coagulation and deposition of a processing agent contained in aprocessing liquid, and a colorant can be prevented during a long-termstorage of the printing liquid.

Specific examples of the water-soluble organic solvent include, in thecase of poly-hydric alcohols, ethylene glycol, diethylene glycol,propylene glycol, butylene glycol, triethylene glycol, 1,5-pentanediol,1,2,6-hexanetriol and glycerine.

The water-soluble organic solvent may be a glycol ether. Examplesthereof include ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, diethylene glycolmonomethyl ether, diethylene glycol monoethyl ether, diethylene glycolmonobutyl ether, propylene glycol monobutyl ether, dipropylene glycolmonobutyl ether, and poly-hydric alcohol derivatives such as an ethyleneoxide adducts of diglycerine.

The water-soluble organic solvent may be a nitrogen-containing solvent.Examples thereof include pyrrolidone, N-methy-2-pyrrolidone,cyclohexylpyrrolidone and triethanolamine.

The water-soluble organic solvent may be a sulfur-containing solvent.Examples thereof include thiodiethanol, thiodiglycerol, sulfolane anddimethyl sulfoxide. Additionally, propylene carbonate, ethylenecarbonate can also be used together. Alcohols such as ethanol, isopropylalcohol, butyl alcohol, and benzyl alcohol can also be used. The contentof the water-soluble organic solvent is from 1 to 60 parts by mass,preferably from 5 to 40 parts by mass.

Further, a surfactant may be added to a printing liquid. As thesurfactant, a compound having a structure which includes a hydrophilicpart and a hydrophobic part together in the molecule can be used. Thesurfactant may be anionic, cationic, amphoteric or nonionic.

Examples of the anionic surfactant include alkylbenzenesulfonates,alkyphenylsulfonates, alkylnaphthalenesulfonates, salts of higher fattyacids, sulfate ester salts of higher fatty acid esters, sulfonate saltsof higher fatty acid esters, sulfate ester salts of higher alcoholethers, sulfonate salts of higher alcohol ethers, higheralkylsulfosuccinate salts, higher alkylphosphate ester salts, andphosphate ester salts of higher alcohol ethylene oxide adducts. Forexample, dodecylbenzenesulfonate salts, tetradecylbenzenesulfonatesalts, isopropylnaphthalenesulfonate salts,monobutylphenylphenolmonosulfonate salts, monobutylbiphenylsulfonatesalts, monobutylbiphenylsulfonate salts, dibutylphenylphenoldisulfonatesalts can also be effectively used.

Examples of the nonionic surfactant include polypropylene glycolethylene oxide adducts, polyoxyethylene nonylphenyl ethers,polyoxyethylene octylphenyl ethers, polyoxyethylene dodecylphenylethers, polyoxyethylene alkyl ethers, polyoxyethylene fatty acid esters,sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters,fatty acid alkylolamides, acetylene glycol, oxyethylene adducts ofacetylene glycol, aliphatic alkanolamides, glycerin esters and sorbitanesters.

The cationic surfactant may be a tetraalkyl ammonium salt, an alkylaminesalt, a benzalkonium salt, an alkylpyridium salt or an imidazolium salt,and examples thereof include dihydroxyethylstearylamine,2-heptadecenyl-hydroxyethylimidazoline, lauryldimethylbenzylammoniumchloride, cetylpyridinium chloride and stearamidemethylpyridiumchloride.

Silicone-based surfactants such as polysiloxane oxyethylene adducts, andfluorine-based surfactants such as salts of perfluoroalkylcarboxylicacids, perfluoroalkylsulfonate salts and oxyethylene perfluoroalkylethers, and bio-surfactants such as spiculisporic acid, rhamnolipid andlysolecithin, can also be used.

The amount of the surfactant added in a printing liquid is preferablyless than 10 parts by mass. When the amount is 10 parts by mass orlarger, optical density deteriorates and the storage stability of aprinting liquid deteriorates in some cases.

In addition, for the purpose of controlling the properties of a printingliquid such as improvement in dischargeability, the following compoundscan be added: polyethyleneimine, polyamines, polyvinylpyrrolidone,polyethylene glycol, cellulose derivatives such as ethylcellulose andcarboxylmethylcellulose, polysaccharides and derivatives thereof, otherwater-soluble polymers, polymer emulsions such as acrylic polymeremulsion and polyurethane-based emulsion, cyclodextrin, large ringamines, dendrimer, crown ethers, urea, derivatives of urea, acetamideand the like.

In order to regulate electric conductivity and pH, compounds of alkalimetals such as potassium hydroxide, sodium hydroxide and lithiumhydroxide, and nitrogen-containing compounds such as ammonium hydroxide,triethanolamine, diethanolamine, ethanolamine and2-amino-2-methyl-1-propanol can be used.

Antioxidants, fungicides, viscosity regulating agents, conductiveagents, ultraviolet absorbers can also be used, if necessary.

—Coagulation-Thickening Preventing Agent—

The coagulation-thickening preventing agent used in the inkjet liquidtreatment method of the invention has a function of preventing thereaction of a metal ion contained in the first printing liquid with ananionic compound contained in the second printing liquid, and preventingcoagulation and thickening of the mixture which includes these twoprinting liquids. The coagulation-thickening preventing agent reactswith the metal ion by chelating as described later, to form a reactionproduct with excellent solubility in the mixture, which is an aqueousliquid.

The coagulation-thickening preventing agent is not limited to particularcompounds and may be any compound that has the function. Specifically,the agent may be a chelating agent which chelates the polyvalent metalion or a masking agent which masks the polyvalent metal ion and protectsit from the anionic compound.

The coagulation-thickening preventing agent may be acetylacetone,adenine, 5′-adenosine triphosphate, 2-aminoethanol, 2-aminoethanethiol,imidazole, ethylamine, ethylenediamine, catechol, citric acid,glycylglycine, glycine, glutamic acid, acetic acid, L-2,4-diaminobutyricacid, diethylenetriamine, L-cysteine, dibenzo-18-crown-6, oxalic acid,triethylenetetramine, picolic acid, histidine, 2,2′-bipyridyl, pyridine,1,10-phenanthroline, L-phenylalanine, phenol, phthalic acid, malonicacid, or a salt thereof.

Among these coagulation-thickening preventing agents, particularly,nitrilotriacetic acid, N,N-(2-hydroxyethyl)-glycine,ethylenediamine-N,N,N′,N′-tetraacetic acid, dicarboxylic acid,tricarboxylic acid, phosphoric acid and salts thereof are preferable.The dicarboxylic acids (including salts thereof) may be preferablytartaric acids, and the tricarboxylic acids (including salts thereof)may be preferably citric acids. These coagulation-thickening preventingagents effectively chelate or mask particularly a magnesium ion.

Examples of the citric acids include citric acid, lithium citrate,potassium citrate, potassium dihydrogen citrate, sodium citrate, sodiumdihydrogen citrate and ammonium citrate, and examples of the tartaricacids include tartaric acid, potassium tartrate and sodium potassiumtartrate.

The coagulation-thickening preventing agent may be selected depending onthe composition of the printing liquid which is to be treated,particularly depending on the combination of the polyvalent metal ionand the anionic compound so that the function of the agent is optimized.When replenishing of the coagulation-thickening preventing agent cannotbe conducted at arbitrary timing, which is the case in an inkjetrecording apparatus, the amount of the coagulation-thickening preventingagent stored beforehand in the inkjet recording apparatus can beselected depending on the amount of the printing liquid used in theinkjet recording apparatus.

The coagulation-thickening preventing agent can be used in a form of asolution in a solvent (hereinafter, abbreviated as“coagulation-thickening preventing agent solution” in some cases),whilst it can also be used in a form of raw liquid or solid.Particularly when the coagulation-thickening preventing agent should beused as an aqueous solution, evaporation of moisture, change inconcentration, and deposition of the coagulation-thickening preventingagent can be suppressed by using the agent in a form of a solution whosesolvent is water or a non-volatile organic solvent.

The non-volatile organic solvent used in the coagulation-thickeningpreventing agent solution may be a known compound, and typical examplesthereof include poly-hydric alcohols and glycol ethers. Specificexamples thereof include, in the case of the poly-hydric alcohols,ethylene glycol, diethylene glycol, propylene glycol, butylene glycol,triethylene glycol, 1,5-pentanediol, 1,2,6-hexanetriol and glycerine.

The non-volatile organic solvent may be a glycol ether. Examples thereofinclude ethylene glycol monomethyl ether, ethylene glycol monoethylether, ethylene glycol monobutyl ether, diethylene glycol monomethylether, diethylene glycol monoethyl ether, dieithylene glycol monobutylether, propylene glycol monobutyl ether, dipropylene glycol monobutylether, and polyhydric alcohol derivatives such as an ethylene oxideadducts of diglycerine.

The non-volatile organic solvent may be a nitrogen-containing solventsuch as pyrrolidone, N-methy-2-pyrrolidone, cyclohexylpyrrolidone ortriethanolamine, or a sulfur-containing solvent such as thiodiethanol,thiodiglycerol, sulfolane or dimethyl sulfoxide. To acoagulation-thickening preventing agent solution, preservatives,fungicides and germicides can be further added, if necessary.

Further, a surfactant can also be added to a coagulation-thickeningpreventing agent solution. Examples of the surfactant are the same asthe examples of the surfactant that is used in a printing liquid.

(Inkjet Recording Apparatus, Inkjet Liquid Storing Tank, Inkjet LiquidStoring Liquid Absorber, Inkjet Liquid Treatment Apparatus)

Next, an inkjet recording apparatus, inkjet liquid storage tank (liquidstorage tank), liquid absorber for inkjet liquid storage (liquidabsorber) and inkjet liquid treatment apparatus (liquid treatmentdevice) of the invention utilizing the inkjet liquid treatment method ofthe invention as described above will be described below.

The inkjet recording apparatus of the invention utilizes the inkjetliquid treatment method of the invention described above, andspecifically, the apparatus may preferably have a constitution asdescribed below:

The inkjet recording apparatus has a constitution using at least onefirst printing liquid and at least one second printing liquid, asprinting liquids,

wherein the apparatus at least has

-   -   a recording head comprising a plurality of nozzles that fires at        least one liquid and    -   a liquid treatment device comprising a liquid storage part that        recovers the printing liquids fired from the recording head in a        non-printing period and stores the liquids

wherein the liquid storage part stores a mixture comprising at least oneof the first printing liquid(s) and at least one of the second printingliquid(s) fired from the recording head in a non-printing period,

wherein the mixture stored in the liquid storage part includes acoagulation-thickening preventing agent which prevents the reaction ofthe metal ion with the anionic compound.

Since the inkjet recording apparatus of the invention utilizes theinkjet liquid treatment method of the invention, coagulation andthickening of the mixture can be suppressed when a first printing liquidand a second printing liquid are treated in a mixed state in theapparatus. The treatment may be disposal of the printing liquids.

In the inkjet recording apparatus of the invention, the mixture storedin a liquid storage part includes a coagulation-thickening preventingagent. However, timing of addition of the coagulation-thickeningpreventing agent to a mixture is not particularly restricted.

The coagulation-thickening preventing agent can be added to at least oneliquid selected from the first printing liquid, the second printingliquid and the mixture including both liquids. The timing of addition isat any time during the period after the first printing liquid and thesecond printing liquid are fired from the recording head in anon-printing time but before both liquids are mixed and finally storedin the liquid storage part.

Specifically, the coagulation-thickening preventing agent (orcoagulation-thickening preventing agent solution) may be previouslystored in the liquid storage part so that it will be able to be mixedwith a mixture including both the first and second printing liquids. Inthis case, when the mixture (or the first printing liquid and the secondprinting liquid before mixing) is recovered into the liquid storage partthrough a tube and stored in the liquid storage part, the mixture ismixed with the coagulation-thickening preventing agent (orcoagulation-thickening preventing agent solution). Therefore,coagulation and thickening of the mixture can be prevented.

When the mixture is recovered through a tube or the like but acoagulation-thickening preventing agent (or a coagulation-thickeningpreventing agent solution) is not added until a mixture reaches theliquid storage part, it is preferable to store a coagulation-thickeningpreventing agent (or a coagulation-thickening preventing agent solution)near a liquid inlet of a liquid storage part so that the agent can bemixed with the mixture. The term “liquid inlet” used herein refers tothe part where the tube or pipe through which the mixture is transferredto the liquid storage part is connected the liquid storage part). If acoagulation-thickening preventing agent (or a coagulation-thickeningpreventing agent solution) is not stored near a liquid inlet,coagulation and thickening may occur near the liquid inlet to disturbflowing of the mixture into the liquid storage part.

The form of the liquid storage part used in the inkjet recordingapparatus of the invention is not particularly restricted providing itcan store the printing liquids fired from a recording head innon-printing periods without scattering of the liquids into an inkjetrecording apparatus. The form may be, for example, a form of sealedvessel, or a liquid absorber including a water-absorbing substancecapable of absorbing and retaining liquid with a weight which is severalto dozens-fold or more of self weight such as a known polymer gel or afiber. When a liquid absorber is used, the liquid absorber may be placedpreferably in a liquid storing tank.

Two or more liquid storage parts may be provided in an inkjet apparatus.However, preferably, only one liquid storage part may be provided in theinkjet recording apparatus of the invention. More preferably, the liquidstorage part may be a one-chamber type liquid storage part having, in aliquid storage part, no partition or the like for separately storingevery printing liquid fired from a recording head in non-printingperiods. In other words, the liquid storage part stores all kinds ofprinting liquids in a mixed state.

In the inkjet recording apparatus of the invention, coagulation andthickening in the liquid storage part can be suppressed even when allkinds of printing liquids used for printing are stored in a mixed state.Therefore, even if only one one-chamber type liquid storage part isprovided, the amount of the liquid actually storable is not smaller thanthe designed storage volume of a liquid storage part. This contrastswith conventional inkjet printers in which the amount of the liquidstorable decreases owing to clogging and the like caused by coagulationand thickening. Because of this fact, according to the invention, thesize of the liquid storage part can be made smaller than conventionalsize.

When only one one-chamber type liquid storage part is used as a liquidtreatment device, it is also possible to use only one recovering pipesuch as a tube to recover the printing liquids fired from the recordinghead and to introduce the liquids to the liquid storage part. Inparticular, when a coagulation-thickening preventing agent (or acoagulation-thickening preventing agent solution) is added almostsimultaneously with the firing of a printing liquid from a recordinghead in non-printing periods, clogging owing to coagulation andthickening of the mixture including both the first and second printingliquids in the recovering pipe can be certainly prevented. Therefore,only one recovering pipe connected to the liquid storage part can beused in the constitution.

On the other hand, if printing liquids that can coagulate and thickenwhen mixed with each other are used, a liquid treatment device providedin a conventional inkjet recording apparatus has a plurality of liquidstorage parts in order to prevent clogging in the liquid storage partand the covering pipe, or uses a liquid storage part whose interiorportion is partitioned into two or more chambers. Further, in aconventional inkjet recording apparatus, a plurality of recovering pipesconnected to a liquid storage part are provided. Therefore, the liquidtreatment device is likely to be complicated and large, and the numberof the parts constituting the liquid treatment device increases toelevate the production cost.

However, the inkjet recording apparatus of the invention utilizes theinkjet liquid treatment method of the invention. Accordingly, the liquidtreatment device in the inkjet recording apparatus can be simplified andsmall and can be produced at low cost, as described above.

As described above, a coagulation-thickening preventing agent (or acoagulation-thickening preventing agent solution) can be added to atleast one liquid selected from the first printing liquid, the secondprinting liquid and the mixture including both liquids, at any timeduring the period after the first printing liquid and the secondprinting liquid are fired from the recording head in a maintenanceperiod but before both liquids are mixed and finally stored in theliquid storage part.

However, in order to more efficient suppress and prevent coagulation andthickening of the mixture caused by the reaction of the polyvalent metalion with the anionic compound, it is preferable to add acoagulation-thickening preventing agent (or coagulation-thickeningpreventing agent solution) at the time when the first printing liquidand the second printing liquid are mixed or immediately after themixing. It is particularly preferable to add a coagulation-thickeningpreventing agent (or a coagulation-thickening preventing agent solution)to the first printing liquid at any time during the period from justafter the firing of the first printing liquid from the recording head tojust before the mixing of the first printing liquid with a secondprinting liquid.

When a coagulation-thickening preventing agent (or acoagulation-thickening preventing agent solution) is added to themixture including both the first and second printing liquids at thetiming described above or added to the first printing liquid during theperiod from just after the firing of the first printing liquid from therecording head to just before the formation of the mixture (being mixedwith a second printing liquid), the reaction of the polyvalent metal ionwith the anionic compound can be prevented more effectively andsuppression of the coagulation and thickening of the mixture becomeseasier.

The way of adding a coagulation-thickening preventing agent to the firstprinting liquid, second printing liquid or mixture is not particularlyrestricted. Known methods can be utilized.

For example, the coagulation-thickening preventing agent may be added bya coagulation-thickening preventing agent solution feeding apparatusconnected to the middle of a recovering pipe or connected to the liquidstorage part.

However, in the inkjet recording apparatus of the invention, it ispreferable to add the coagulation-thickening preventing agent solutionby a liquid firing apparatus provided with a nozzle that fires thecoagulation-thickening preventing agent solution.

The liquid firing apparatus may be placed so that the apparatus canpreferably move along a scanning line that the recording head movesalong in printing and maintenance (non-printing). The constitution ofthe liquid firing apparatus may be similar to that of the recording headused for printing. Hence, the recording head for printing and thecoagulation-thickening preventing agent solution imparting head (theliquid discharging apparatus) can be provided on the scanning line.

The generally used recording head has liquid storing cartridges eachstoring two or more liquids and each liquid can be fired from a separatenozzle. In such a case, the following constitution is possible: at leastone printing liquid is contained in a cartridge and one of the othercartridges contains the coagulation-thickening preventing agentsolution. Specifically, the following constitution is possible: arecording head comprises a liquid storage cartridge that contains thecoagulation-thickening preventing agent solution and liquid storagecartridges containing cyan, magenta, yellow and black inks respectively.In this constitution, the recording head also has a function as acoagulation-thickening preventing agent solution imparting head.Consequently, the structure of the inkjet recording apparatus can befurther simplified.

Maintenance of a recording head can be conducted by utilizing a knownmethod in non-printing periods. For example, when a printing liquid in anozzle of the recording head is fired by dummy jet in non-printingperiods, a recording head is moved, before the printing liquid can befired (dummy jet), to such a position that the printing liquid fired canbe recovered to the liquid storage part of the liquid treatment deviceat the maintenance part.

Alternatively, when a printing liquid in a nozzle of the recording headis fired by suction in non-printing periods, the printing liquid can besucked via a cap member connected via a suction pump and tube to theliquid storage part of the liquid treatment device. The cap member isplaced so that it is closely adhered to the nozzle surface of therecording head which moved to the maintenance part in a maintenanceperiod.

When the recording head and the maintenance head for adding acoagulation-thickening preventing agent solution are used, for example,the recording head is moved to a position in a maintenance part at whicha printing liquid can be fired, then a printing liquid is fired by dummyjet or suction, then a coagulation-thickening preventing agent solutionimparting head is moved to the same position and acoagulation-thickening preventing agent solution is fired.

In this case, the following sequence is naturally possible: first, therecording head moved to the maintenance part and only the first printingliquid is fired; then a coagulation-thickening preventing agent solutionimparting head is moved to the maintenance part and acoagulation-thickening preventing agent solution is fired; then therecording head is again moved to the maintenance part and only thesecond printing liquid is fired. In this sequence, substantially, onlyafter the addition of the coagulation-thickening preventing agentsolution to the first printing liquid, the second printing liquid isfurther mixed. Therefore, coagulation and thickening of the mixture canbe suppressed more efficiently.

When the recording head also has the function of thecoagulation-thickening preventing agent solution imparting head, thesurfaces of the nozzles for the respective liquids (the first printingliquid, the second printing liquid, and the coagulation-thickeningpreventing agent solution), which are to be fired from the recordinghead, are moved to the liquid recovering port that recovers the firedliquids so that the first printing liquid, the coagulation-thickeningpreventing agent solution and the second printing liquid can be fired inthis order as described above.

Other than the firing of a printing liquid in a nozzle by dummy jet-andthe suction as described above, a wiper can also be provided to wipe thenozzle surface of the recording head which has been moved to themaintenance part in a maintenance period. Further, it is also possibleto perform maintenance that includes a combination of known recordinghead maintenance methods such as the dummy jet, suction and wipingdescribed above.

In the above, the invention is described mainly using a polyvalent metalion and an anionic compound as an example of the compounds that reactwith each other to cause coagulation and thickening. However, theinvention can be worked out as long as two liquids that react with eachother to cause coagulation and thickening are used, and thecoagulation-thickening preventing agent is appropriately selectedaccording to the combination of the liquids.

EXAMPLES

The present invention will be explained in more detail by the examplesbelow, however, the invention is by no means limited to these examples.

I) Preparation of Ink and Coagulation-Thickening Preventing AgentSolution

The preparation of an ink include the following: a water-soluble organicsolvent, other additives and an ion exchange water are added inappropriate amounts to a colorant solution to prepare a solutionincluding the respective materials in given amounts; then the solutionis stirred; then a black ink is filtrated through a filter with a meshsize of 1 μm and a color ink is filtrated through a filter with a meshsize of 0.5 μm to obtain each ink with respective color. Acoagulation-thickening preventing agent solution is prepared by addingnecessary components in given amounts, mixing and stirring thecomponents, and filtering the solution through a filter with a mesh sizeof 0.5 μm.

The raw materials used for the preparation of the inks of respectivecolors of an ink set 1 composed of black, cyan, magenta and yellow andthe amounts of the materials to be used are shown below. The rawmaterials used for the preparation of a coagulation-thickeningpreventing agent solution land the amounts of the materials to be usedare also shown below.

—Ink Set 1— <Black ink> CABOJET 300 (anionic colorant, manufactured by5.0 parts by mass Cabot Corporation): 1,5-pentanediol: 10 parts by massthiodiethanol: 10 parts by mass diethylene glycol monoethyl ether: 2.0parts by mass thiourea: 3.0 parts by mass isopropyl alcohol: 4.0 partsby mass ion exchange water: 66 parts by mass

<Cyan ink> C.I. Acid Blue-9: 3.5 parts by mass 1,5-pentanediol: 10 partsby mass thiodiethanol: 10 parts by mass diethylene glycol monoethylether: 2.0 parts by mass thiourea: 3.0 parts by mass isopropyl alcohol:4.0 parts by mass sodium hydroxide: 0.03 parts by mass magnesiumsulfate: 1.0 part by mass (corresponding to about 2000 ppm of magnesium)ion exchange water: 66.47 parts by mass

This ink includes magnesium ions as the polyvalent metal ion, and thecontent thereof is about 2000 ppm. <Magenta ink> ILM-377 (manufacturedby ILFORD): 3.0 parts by mass 1,5-pentanediol: 10 parts by massthiodiethanol: 10 parts by mass diethylene glycol monoethyl ether: 2.0parts by mass thiourea: 3.0 parts by mass isopropyl alcohol: 4.0 partsby mass sodium hydroxide: 0.03 parts by mass magnesium sulfate: 1.0 partby mass (corresponding to about 2000 ppm of magnesium) ion exchangewater: 66.97 parts by mass

This ink includes magnesium ions as the polyvalent metal ion, and thecontent thereof is about 2000 ppm. <Yellow ink> C.I. Acid Yellow-23: 3.0parts by mass 1,5-pentanediol: 10 parts by mass thiodiethanol: 10 partsby mass diethylene glycol monoethyl ether: 2.0 parts by mass thiourea:3.0 parts by mass isopropyl alcohol: 4.0 parts by mass sodium hydroxide:0.03 parts by mass magnesium sulfate: 1.0 part by mass (corresponding toabout 2000 ppm of magnesium) ion exchange water: 66.97 parts by mass

These inks each include magnesium ions as the polyvalent metal ion, andthe content thereof is about 2000 ppm. -Coagulation-thickeningpreventing agent solution 1- sodium citrate: 20 parts by mass diethyleneglycol: 20 parts by mass ion exchange water: 60 parts by massII) EvaluationII-1) Inkjet Recording Apparatus

Printing and maintenance of a recording head are conducted by the inkjetrecording apparatus explained below, using only the ink set or the inkset and the coagulation-thickening preventing agent in combination.Presence or absence of abnormalities of the waste liquid processingsystem of the maintenance part and the quality of an image printed areevaluated.

The inkjet recording apparatus used utilizes a thermal ink jet modecapable of performing full color printing, and has an experimental modelrecording head of 400 dpi, 256 nozzles that fire a black ink and acoagulation and thickening-preventing liquid, and an experimental modelrecording head of 800 dpi, 512 nozzles that fire color inks (cyan,magenta, yellow).

In this inkjet recording apparatus, a maintenance apparatus is providedwhich comprises a waste liquid processing device comprising a pluralityof caps that recover printing liquids and coagulation-thickeningpreventing agent solutions in nozzles of the recording heads by dummyjet and suction, a waste liquid storage part connected by a tube via asuction pump to the caps, and a wiper that wipes the nozzle surface ofthe recording head.

Printing liquids and coagulation-thickening preventing agent solutionsfired during suction or dummy jet and recovered from the cap part areall recovered through the tube to one waste liquid storing tankcontaining a liquid absorber made of a polyester film. The liquidabsorber has an ability to absorb liquid in an amount of 600 ml atmaximum, and set beforehand in the waste liquid storing tank afterabsorbing 60 ml of the coagulation-thickening preventing agent solution.

Suction of printing liquids and coagulation-thickening preventing agentsolutions from the recording head is conducted by driving a suction pumpso that a constant amount of liquid is sucked wherein each cap providedcorresponding to each nozzle surface that fire each liquid faces thenozzle surface when each recording head is moved to the maintenance partin non-printing periods. On the other hand, dummy jet of a printingliquid or a coagulation-thickening preventing agent solution from arecording head is conducted by firing the printing liquid or acoagulation-thickening preventing agent solution from the nozzle surfaceinto the cap during no-printing periods.

The movement of the dummy jet is so programmed that, in printing animage, a recording head becomes non-printing condition and moves to amaintenance part appropriately. After the movements of the suction ordummy jet, the movements of the recording head and the maintenance partare programmed so that wiping of the nozzle surface is conducted.

For printing of an image, roll paper is used as a recording paper, andprinting of an image is conducted in an environment of 23° C. and 55%RH. In this case, the firing of printing liquids and thecoagulation-thickening preventing agent from the recording head isperformed while a drop of each liquid is formed by applying a pluralityof pulses to the liquid. The amount per drop is about 18 pl in the caseof a black ink and a coagulation-thickening preventing agent solutionand about 6 pl in the case of color inks.

II-2) Presence or Absence of Abnormalities of Waste Liquid ProcessingSystem and Quality of Image

On a black image part, three colors of cyan, magenta and yellow arecontinuously primer-printed for carriage 10 reciprocations in lump twoway with a coverage of 16.7% for each of cyan, magenta and yellow basedon 100% coverage of black, and 100% coverage patch printing iscontinuously conducted for carriage 10 reciprocations at one-passbi-directional printing so that black and cyan, black and magenta, andblack and yellow are adjacent in this order. FX-P paper is processed inthe form of roll and used as the paper for the printing.

Thereafter, a dummy jet operation is conducted in which a black ink anda coagulation-thickening preventing agent solution are fired 1000 timeseach and color inks are fired 3000 times each from all nozzles into thecaps.

When this printing and dummy jets are repeated 1000 times alternately,the system is left for 48 hours while the nozzle surface of therecording head is covered with the caps. Thereafter, the printing liquidand the coagulation-thickening preventing agent are sucked each in anamount of 0.5 ml from the nozzle surface corresponding to each liquid inall heads by a suction pump. Then, the printing-dummy jet-suctionoperation is again repeated 200 times. In each suction, the presence ofclogging in the suction pump or tube and the occurrence counterflow oroverflow from the waste liquid storing tank are observed.

If the evaluation is conducted without using a coagulation-thickeningpreventing agent solution, the dummy jet and suction are performed bydischarging only inks from the recording head.

With respect to the resulted printing pattern, the concentration of theblack image with primer-printing with color inks is observed.Inter-ColorBleed between black and cyan 100% coverage patch, betweenblack and magenta 100% coverage patch, or between black and yellow 100%coverage patch, are also observed.

III) Evaluation Result

The results regarding the presence or absence of abnormalities of thewaste liquid processing system and the quality of an image are shownbelow. In Example 1 in which a coagulation-thickening preventing agentsolution is used together with the ink set 1 composed of a firstprinting liquid (color ink) and a second printing liquid (black ink),clogging does not occur in the suction pump and tube and the counterflowand overflow from the waste liquid storing tank are not observed.

On the other hand, in Comparative Example 1 using only the ink set 1,the movement was abnormal at 10-th pump suction, and as a result ofdecomposition, local adhering of a coagulated substance in the tube isobserved, and the accumulation of a coagulated substance in the liquidabsorber in the waste liquid storing tank is observed around the inletat which the end of the tube is connected to the waste liquid storingtank.

In both Example 1 and Comparative Example 1, the ink set 1 including thefirst printing liquids (color inks) and the second printing liquid(black ink) is used. Therefore, the concentration of the black image ishigh and Inter-color bleed between colors is not observed. Summary ofthese results are shown in Table 1. TABLE 1 Coagulation- Presence orabsence of Inter-colorBleed thickening preventing abnormalities of wasteColor primer-printing between black ink and Ink set agent solutionliquid processing part Black image density color inks Example 1 Ink set1 Coagulation- Absence 1.55 None thickening preventing agent solution 1Comparative Ink set 1 — Presence 1.55 None Example 1 (at 10-th suction)

1-26. (canceled)
 27. An inkjet liquid storage tank used in an inkjetrecording apparatus, wherein the apparatus uses at least one firstprinting liquid including a polyvalent metal ion and at least one secondprinting liquid including an anionic compound which is capable ofreacting with the metal ion to cause coagulation and thickening if mixedwith the first printing liquid, wherein the apparatus comprises: arecording head comprising a plurality of nozzles which fire at least oneliquid; and a liquid treatment device comprising a liquid storage tankthat recovers the printing liquids fired from the recording head duringa non-printing period and stores the printing liquids, wherein a mixtureincluding at least one of the first printing liquid(s) and at least oneof the second printing liquid(s) fired from the recording head duringthe non-printing period is stored in the liquid storage tank, andwherein the tank contains a coagulation-thickening preventing agentwhich prevents the reaction of the metal ion with the anionic compound,the agent being contained in a state which allows the agent to mix withthe mixture.
 28. A liquid absorber for an inkjet liquid storage used inan inkjet recording apparatus, wherein the apparatus uses at least onefirst printing liquid including a polyvalent metal ion and at least onesecond printing liquid including an anionic compound which is capable ofreacting with the metal ion to cause coagulation and thickening if mixedwith the first printing liquid, wherein the apparatus comprises: arecording head comprising a plurality of nozzles which fire at least oneliquid; and a liquid treatment device having a liquid storage part thatrecovers the printing liquids fired from the recording head during anon-printing period in order to maintain the recording head and storesthe printing liquids, wherein the liquid storage part includes a liquidabsorber for inkjet liquid storage, the absorber being able to store theat least one liquid fired from the nozzles, wherein a mixture includingat least one of the first printing liquid(s) and at least one of thesecond printing liquid(s) discharged from the recording head during thenon-printing period is stored in the liquid storage part, and whereinthe tank contains a coagulation-thickening preventing agent whichprevents the reaction of the metal ion with the anionic compound, theagent being contained in a state which allows the agent to mix with themixture.
 29. (canceled)
 30. A method according to claim 27, wherein thecoagulation-thickening preventing agent is a chelating agent thatchelates the metal ion or a masking agent that masks the metal ion andprotects the metal ion from the anionic compound.
 31. A method accordingto claim 27, wherein the coagulation-thickening preventing agent is atleast one selected from the group consisting of nitrilotriacetic acid,N,N-(2-hydroxyethyl)-glycine, ethylenediamine-N,N,N′,N′-tetraaecticacid, dicarboxylic acids, tricarboxylic acids, phosphoric acid and saltsthereof
 32. A method according to claim 31, wherein the dicarboxylicacids and the salts thereof are at least one selected from tartaricacids including tartaric acid, potassium tartrate and sodium potassiumtartrate, and the tricarboxylic acids and the salts thereof are at leastone selected from citric acids including citric acid, lithium citrate,potassium citrate potassium dihydrogen citrate, sodium citrate, disodiumhydrogen citrate and triammonium citrate.
 33. A method according toclaim 30, wherein the coagulation-thickening preventing agent is used ina form of a solution in a liquid including a non-volatile organicsolvent and water.
 34. A method according to claim 33, wherein thecoagulation-thickening preventing agent comprises a surfactant.
 35. Amethod according to claim 34, wherein the non-volatile organic solventis at least one selected from the group consisting of poly-hydricalcohols and glycol ethers.
 36. A method according to claim 27, whereinthe content of the polyvalent metal ion included in the first printingliquid is 100 ppm or higher.
 37. A method according to claim 27, whereinthe content of the polyvalent metal ion included in the first printingliquid is 500 ppm or higher.
 38. A method according to claim 28, whereinthe coagulation-thickening preventing agent is at least one selectedfrom the group consisting of nitrilotriacetic acid,N,N-(2-hydroxyethyl)-glycine, ethylenediamine-N,N,N′,N′-tetraaceticacid, dicarboxylic acids, tricarboxylic acids, phosphoric acid and saltsthereof.
 39. A method according to claim 38, wherein the dicarboxylicacids and the salts thereof are at least one selected from tartaricacids including tartaric acid, potassium tartrate and sodium potassiumtartrate, and the tricarboxylic acids and the salts thereof are at leastone selected from citric acids including citric acid, lithium citrate,potassium citrate, potassium dihydrogen citrate, sodium citrate,disodium hydrogen citrate and triammonium citrate.
 40. A methodaccording to claim 28, wherein the content of the polyvalent metal ionincluded in the first printing liquid is 100 ppm or higher.
 41. A methodaccording to claim 28, wherein the content of the polyvalent metal ionincluded in the first printing liquid is 500 ppm or higher.